Brake Fluid: Heat Reaction

[khansmith]

Hi all:
When my cobra is cooled down, I notice the car rolls easily if I push it. However, if I go on a slow-ish cruise for an hour or so on a hot day (like today, it was in the 90's) I notice that the brakes start to drag on the rotors to a point where I can't push the car like I can when it is cooled down.. My brake lines route near my jet coated headers and I am using racing brake fluid. Anyway, could the brake fluid be expanding and putting pressure on the brake pistons?

Thank you for your time and thought.

Khan

[strictlypersonl]

There is a return port in the master cylinder that should be open when the pedal is released. The port allows excess fluid to backflow into the reservoir. It's possible that the linkage is preventing the master cylinder piston from doing its thing, or the MC is defective. Another alternative is a defective caliper, so check whether only one side is dragging by comparing the rotor temperature from side to side.

[bobcowan]

I agree with above. Either a caliper is hanging, or the piston in the MC is not fully retracted.

[khansmith]

Thanks guys. Sounds like heat is not the enemy here
.

[khansmith]

I checked the heat on all the rotors adn they were all within 15 degrees of one another. After about an hour of cooling down, the car rolled without resistance.

[Bob In Ct]

Sometimes the rubber in the brake lines swells with age. The fluid is under enough pressure to apply the brakes but the fluid will not flow back when the brakes are released. Changing the rubber brake lines would be necessary.

bob

[Z-linkCobra]

I would say your calipers are sticking. Not so much the pistons in the calipers but the sliders. Some years back when I was running the dragster quite a bit I started experiencing a soft pedal in the brakes. Right when I would stab the brake the first time it would almost go to the floor...pump it one time and had plenty of pedal. As the day prgressed and the temp rose the brakes would start to drag a little. We ran 6 piston Mark Williams calipers with a solid plate(no sliders). What I found was a slightly bent mounting plate causing deflection of the rotor. Thats when the rotor and the caliper are not inline with one another.

Dont know what kind of caliper mounting plates you have but make sure they are lined up properly. Heat will warp things in unusual ways and have you chasing your tail.

Just something from my past experiences.

[Kit Cars Mexico]

Khan,

I had the same problem, and I solved it by loosening a little bit the brake bar on pedals.

Alfredo

[Excaliber]

I had a bad rubber clutch release hose (same principle as brakes, hydraulic pressure). I would push in the clutch pedal, clutch would release, I'd let out the clutch pedal and SLOWLY the clutch would begin to engage.

The hose was all nasty inside, the crap inside acting like a one way valve. Pressure out OK, but it would return in it's own sweet time. Eventually the clutch would engage and were off, then try wait when you shift to second, again for third, etc.

Austin Healey 3000, decades old hose, not likely the problem here, ya just brought back that memory.